The structures and stabilities of gold clusters with up to 14 atoms have been determined by density-functional theory. The structure optimizations and frequency analysis are performed with the Perdew-Wang 1991 gradient-corrected functional combined with the effective core potential and corresponding valence basis set (LANL2DZ). The turnover point from two-dimensional to three-dimensional geometry for gold clusters occurs at Au12. The energetic and electronic properties of the small gold clusters are strongly dependent on sizes and structures, which are in good agreement with experiment and other theoretical calculations. The even-odd oscillation in cluster stability and electronic properties predicted that the clusters with even numbers of atoms were more stable than the neighboring clusters with odd numbers of atoms. The stability and electronic structure properties of gold clusters are also characterized by the maximum hardness principle of chemical reactivity and minimum polarizability principle.

Yang Ze-Jin( ) a) † , Cheng Xin-Lu( ) b) , Zhu Zheng-He( ) b) , and Yang Xiang-Dong( ) b)

Quantitative structure -pharmacokinetic/pharmacodynamic (PK/PD) relationship (QSPR) techniques and chemometric methods were employed to classify fluoroquinolones with respect to their activity against Streptococcus pneumoniae. Density functional theory (DFT) was used to calculate a set of molecular descriptors (properties) for 13 synthetic fluoroquinolones. The descriptors were further analyzed using chemometric methods including principal component analysis (PCA), hierarchical cluster analysis (HCA), and stepwise discriminant analysis (SDA). The PCA and SDA methods were employed in order to reduce the dimensionality and select a subset of variables that would be more effective for classifying the fluoroquinolones according to their degree of antipneumococcal activity. The methods of PCA, SDA and HCA were quite efficient to classify 13 compounds in two groups (active and inactive), and the net charge on ring B (Q B ), molecular volume (VOL), and partition coefficient (log P ) were found to be descriptors important for the classification. These methodologies of PCA, SDA and HCA provide a reliable rule for classifying new fluoroquinolones with respect to antipneumococcal activity. The application of the SPP relationship is of considerable value for clinicians, drug developers, and regulators because PK/PD principles form the basis of modern antimicrobial chemotherapy.

The present calculations of three geometry conformation for tetrahydrofuran (THF, C 4 H 8 O) using density functional theory lead to the energy level sequence E(C 1 ) < E(C s ) < E(C 2v ), where, both the geometry symmetry C 2v and C s are probably a transition structure. The C 1 symmetry is the equilibrium conformation, for its energy is the lowest one and it is only possible without the negative harmonic frequency. In C 1 conformation, the 4 of carbon atoms C and oxygen atom O constitute a curved surface or the helix surface. The tetrahydrofuran molecule can be as a simple prototype of deoxyribose and has been reviving a quite deal of interest in radiation damage research. It is well known that the sugar ring of deoxyribose is considered as a plane in most of the references. If the equilibrium conformation of THF is C 1 symmetry with the helix surface, and for the same reason, the sugar ring of deoxyribose would be also the helix surface; this probably causes the double helix of DNA. It is hardly believed that the sugar ring is a plane in deoxyribose.